The present invention relates to a reverberation effect imparting system for use with electronic musical instruments and various audio equipments, and more particularly to a reverberation effect imparting device which has enhanced applicability and controllability.
A typical example of the conventionally-known reverberation effect imparting devices is shown in FIG. 3, in which a delay line 1 delays an input electrical sound signal (hereinafter referred to simply as sound signal) so as to generate a delayed output signal corresponding to an optional delay time to thereby simulate initial reflected sounds. Plural comb filters CF1 to CFn which receive the output signal from the delay line 1 in a parallel fashion are provided for simulating reverberation sounds. One of the comb filters CF1 is composed of a multiplier IMU for variably controlling an input gain ig, a delay line DL for delaying the signal and a feedback loop for filtering the delayed output signal from the delay line DL and feeding the filtered signal to the input side with a variable loop gain lg. This feedback loop includes a low-pass filter LPF for simulating the loss of harmonic components, a multiplier FMU for controlling the variable loop gain lg to simulate a regular level-attenuation (loss) of reverberation sound signals, and a feedback adder (or subtracter) AD.
The delay time of the delay line 1, respective delay times of the comb filters, filtering coefficients and gain coefficients can be variably set so as to obtain desired initial reflected sounds and reverberation sounds. The illustrated example in FIG. 3 is one which is capable of imparting a stereo reverberation effect. For simplification, the following description will be given on only the left channel arrangement of the illustrated device. Delayed output signals corresponding to desired delay times are respectively provided from the delay line D1 in correspondence to a plurality (three in the illustrated example) of initial reverberation sounds. The delayed output signals are variably level-controlled by a multiplier MU1 and summed up by an adder ADD1, so as to obtain a summed initial reflected sound signal. On the other hand, delayed output signals corresponding to desired delay times are provided from the respective delay lines DL of the comb filters CF1 to CFn. The delayed output signals from the delay lines DL are then variably level-controlled by multipliers MU2 and summed up by an adder ADD2, so as to obtain a summed reverberation sound signal. Further, the output signal from the adder ADD2 is passed through serially connected all-pass filters APF1, APF2 to simulate scattering of rear reverberation sound. The initial reflected sound signal and reverberation sound signal output from the adders ADD1 and ADD2, respectively, are added together by an adder ADD3 and further added, in a suitable ratio, with the original sound signal having been imparted no reverberation. The resultant signal is output as a reverberation-effect-imparted signal Lout of the left channel. The above-mentioned operation takes place also in the right channel so that the resultant signal is finally output as a reverberation-effect-imparted signal Rout of the right channel.
U.S. Pat. No. 4,984,276 shows a signal processor employing a waveguide network and describes a technique (waveguide reverberator) in accordance with which an reverberation effect is imparted by using the waveguide network to simulate a physical reverberation mechanism in natural sound space such as audio rooms and concert halls. The disclosed waveguide reverberator forms a closed-type waveguide network by providing output signals from a plurality of parallel-connected waveguides (bidirectional signal transmission means containing delay lines) to a signal junction where the signals are multiplied by respective variable scattering coefficients and added together, and then redistributing the addition result to the waveguides. The disclosed arrangement makes it possible to simulate such complex reverberation where sounds are reflected in a spreaded manner or repeatedly reflected while taking a diffractive roundabout and also to simulate natural reverberation. Further, it is possible to control the reverberation by variably controlling the respective scattering coefficients used in the signal junction section.
However, the conventionally-known reverberation effect imparting devices using the comb filters as shown in FIG. 3 have a significant problem that only reverberation with some peculiarity such as flutter echo is achieved, because they are arranged so that a regular reflected sound is generated by each of the comb filters and complex reflection, i.e., reverberation is created by combinations of the reflected sounds thus generated by the plural comb filters.
In addition, because the initial reflected sounds and reverberation sounds are generated separately, the two kinds of sounds tend to be very poorly connected with each other. Namely, although, in reality, the initial reflected sounds are further reflected to produce additional reverberation, the prior art device is unable to simulate such a state, and thus an unwanted separation occurs between the initial reflected sounds and reverberation sounds.
Moreover, because the prior art device is designed to simulate scattering of rear reverberation sounds by the use of the all-pass filters provided outside the feedback loops of the comb filters, the device can not achieve real simulation of such a case where reverberation density or scattering density varies with time, and thus the simulation tends to be undesirably monotonous.
On the other hand, the second-mentioned device employing the waveguide theory is based on a reverberation effect impartment principle different from that of the conventionally well-known reverberation effect imparting devices employing comb filters as shown in FIG. 3, and therefore it can not utilize the control know-how that has been accumulatively acquired by this type of the well-known reverberation effect imparting devices. Further, some handling difficulties are often encountered in setting various coefficients and delay times, thus making it difficult to set reverberation characteristics as desired by users.